I'm not the best but I'll give it a try:
(defun C:choice (/ COLOR)
(if
(setq COLOR
(acad_colordlg
(cond ; since the number argument needs to be an integer,
; but the CECOLOR System Variable is a text string:
((= (getvar 'cecolor) "BYLAYER") 256)
((= (getvar 'cecolor) "BYBLOCK") 0)
((atoi (getvar 'cecolor)))
); cond
T ; allow BYLAYER/BYBLOCK choices
); acad_colordlg
); setq
(command "Line" "'color" COLOR );;;added transparent command for color and removed the extra quotes
); if
(princ)
); defun